Search

A system of three identical CCD-cameras was developed enabling stereoscopic auroral observations. An image intensifier allows for real-time imaging of auroral arcs with interference or broad-band filters. The combination of a small-angle optics with a CCD-chip of 756 by 580 pixels provides spatial resolutions of auroral small-scale structures down to 20 m. The cameras are controlled by personal computers with integrated global positioning (GPS) modules enabling time synchronization of the cameras and providing the exact geographical position for the portable cameras. Calibration with a standard light source is the basis for quantitative evaluation of images by image processing techniques. The current technical development is the combination with local operating networks (LON) for monitoring camera parameters like voltage and temperature and remote control of parameters like filter positions, mounting tilt angles and camera gain.

The mathematics of emission computed tomography is applied to the three-dimensional reconstruction of the optical emission within an auroral arc. According to general experimental conditions, a very limited angular range and a small number of observers require an iterative back projection method. Parameters for the quantitative correspondence between the original and reconstructed volumes and between the images are defined and using this method, a theoretical arc can be reconstructed with root- mean-square errors of the images of less than 2%. The reconstruction accuracy of the volume can be improved with an increasing number of observers to root-mean-square errors of about 15%. Different geometries are tested but the best results are obtained as long as one observer looks along the magnetic field line through the auroral arc. The calculations confirm the range of suitable observation geometries to within 20 km from the field line through one of the observers.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.